The present invention relates to an optical image pick-up lens, and more particularly to a high performance and low cost optical lens having decreased number of lenses suitable for conventional cameras and cameras using CCD (charge-coupled device) or CMOS (complementary metal-oxide semiconductor) as a sensing element thereof.
With the advancement in scientific technologies, most newly developed electronic products not only have light and compact structure but also provide a variety of functions. For example, image pick-up devices are included not only in digital still cameras, PC (personal computer) cameras, and network cameras, but also in mobile phones, personal digital assistant (PDA), etc. The image pick-up devices require not only good image forming ability but also compact volume and low cost to enable convenient carry of electronic products using the image pick-up devices and to effectively widen the applications of such image pick-up devices.
As an image pick-up device, conventional spherical ground glass lenses have been widely adopted in optical industry field because there is a wide range of materials available for making such lenses and the color aberration thereof can be more easily corrected. However, the spherical ground glass lenses have the disadvantages of uneasy correction of spherical aberration and astigmatic aberration when they are used in cases having a smaller F number and wide angle of field. To improve the above-mentioned drawbacks existed in the conventional spherical ground glass lenses, there have been developed image pick-up devices using aspherical plastic lenses or aspherical molded glass lenses to obtain better image quality, such as the lenses disclosed in U.S. Pat. No. 6,031,670 entitled xe2x80x9cWide-angle Lensxe2x80x9d and Japanese Patent No. P2001-183578A entitled xe2x80x9cImage Pick-up Lensxe2x80x9d. However, the optical image pick-up lenses disclosed in the above-mentioned US and Japanese patents have a length that is still very long. For example, in the lens combination disclosed in Japanese Patent No. P2001-183578A, the distance d from the first side of the first lens to the second side of the second lens is larger than or equal to 0.9f (that is, d greater than 0.9f, where, f is an overall length of the focal lengths of the whole lens combination), preventing the image pick-up lens from having an even smaller volume or lower cost to meet the requirement of light and compact design for all electronic products. The conventional image pick-up lenses therefore have limited applications.
It is a primary object of the present invention to provide an optical image pick-up lens that provides high resolution and has effectively reduced overall lens length, so that the image pick-up lens has smaller volume and lower cost to increase its applications.
To achieve the above and other objects, the optical image pick-up lens of the present invention includes a lens combination consisting of two aspherical molded glass lenses or two aspherical plastic lenses. Both the first and the second lens in the lens combination have at least one of two sides being an aspherical surface. The first lens is a meniscus-shaped lens having a convex surface at a first side or object side thereof, and the second lens is also a meniscus-shaped lens having a convex surface at a second side or image side thereof. And, the lens combination satisfies the following relational expressions:
0.4fxe2x89xa6d less than 0.9f; 
0.5fxe2x89xa6|R3|xe2x89xa6100f; and 
0.01 less than |f2|/|f1| less than 0.9; 
where, f is an overall length of the focal lengths of the whole lens combination; d is a distance from the first side of the first lens to the second side of the second lens; R3 is a radius of curvature of an object side of the second lens; f1 is the focal length of the first lens; and f2 is the focal length of the second lens.